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J. Am. Chem. Soc. 132 (9): 3038–3046 (2010)
Steering S−H and N−H Bond Activation by a Stable N-Heterocyclic Silylene: Different Addition of H2S, NH3, and Organoamines on a Silicon(II) Ligand versus Its Si(II)→Ni(CO)3 Complex
Antje Meltzer , Shigeyoshi Inoue , Carsten Prsang , Matthias Driess
The strikingly different behavior of the ylide-like, N-heterocyclic silylene LSi: (5: L = CH[(C═CH2)CMe(NAr)2]; Ar = 2,6-iPrC6H3) versus its LSi→Ni(CO)3 complex 13 to activate E−H bonds (E = S, N) of small molecules is reported. Remarkably, conversion of 5 with hydrogen sulfide leads exclusively to the first isolable silathioformamide, L′Si(═S)H (16: L′ = CH[C(Me)NAr]2; Ar = 2,6-iPrC6H3) with a donor-supported Si═S double bond and four-coordinate silicon. The latter result demonstrates the unusual ambivalent reactivity of 5 by combining two modes of reactivity involving S−H bond activation and subsequent 1,4- and 1,1-addition, respectively. In addition, 5 can serve as a ligand with well-balanced σ-donor and π-acceptor capabilities toward transition metals. This has been demonstrated by the isolable [Ni0(arene)] complexes 12a−e (arene = MenC6H6−n, n = 0−3), which are ideal precursors for the formation of the corresponding Ni(CO)3 complex 13. The latter activates a S−H bond in hydrogen sulfide, too, but the presence of the Ni(CO)3 moiety governs the formation of the complex 17, bearing an unprecedented β-diketiminate silicon(II) thiol ligand: L′Si(SH): (L′ = CH[C(Me)NAr]2; Ar = 2,6-iPrC6H3). Likewise, the Si(II)→Ni(CO)3 coordination in 13 steers exclusively 1,4-addition of ammonia, isopropylamine, and phenylhydrazine onto the silylene ligand 5, leading to the corresponding β-diketiminate silicon(II) amide or hydrazide complexes L′Si(NHR)→Ni(CO)3 (23a−c: R = H, iPr, N(H)Ph). IR measurements reveal that the carbonyl stretching frequencies of the Ni(CO)3 moiety in 23a−c are shifted to even lower wavenumbers in comparison to those of NHCs or phosphines. In other words, the β-diketiminate silicon(II) amide ligands in 23a−c represent the strongest donors in the series of N-heterocyclic silylenes reported as yet.